Continuous process and apparatus for delignification of cellulosic material



1965 s. A. GUERRIERI 3,215,587

CONTINUOUS PROCESS AND APPARATUS FOR DELIGNIFICATION OF CELLULOSIC MATERIAL Filed Jan. 21, 1963 INVENTOR SAL l/A TOR! A. GUERR/Ek/ BY nZaXW ATTORNEY United States Patent M 3,215,587 CONTINUOUS PROCESS AND APPARATUS FOR DELIGNIFICATION OF CELLULOSIC MATERIAL Salvatore A. Guerrieri, Rowayton, Coma, assignor to The Lurnmus Company, New York, N.Y., a corporation of Delaware Filed Jan. 21, 1963, Ser. No. 252,805 11 Claims. (Cl. 162-19) The present invention relates to an improved process and apparatus for the delignification of cellulosic material, such as wood chips and the like.

In one of its more specific aspects, the present invention relates to continuous vacuum degassing of cellulosic material which has been preheated and dried while maintained in an expanded mass condition.

It has been recognized that air within the interstices or pores of the cellulosic material to be treated is one of the major factors which adversely affects the rate of uniformity of liquor penetration into the cellulosic material. It is known to remove air from cellulosic material by alternate steaming operations at or above atmospheric pressure and venting operations to withdraw a mixture of steam and air from the material. In this manner, a large percentage of the air originally contained in the cellulosic material is removed along with a small amount of the original moisture content of the material. However, a major amount of the original moisture content remains trapped within the pores of the material so that there is relatively little void space for the cooking liquor to occupy, especially if the material to be treated originally had a high moisture content. The cooking liquor which does penetrate into the material must do so by inter-diffusion of the cooking liquor and the water originally contained in the material. Consequently, with materials of high moisture content, the result is reduced chemical concentration within the material and non-uniform penetration.

It has also been proposed to remove air from cellulosic materials by exposing the material to a vacuum. However, such known procedures have not entailed the removal of air from relatively dry material which has been dried by expanded mass techniques.

Accordingly, a principal object of the present invention is to provide process and apparatus for achieving a supply of cellulosic matter in substantially uniform condition, a more rapid and uniform liquor impregnation of cellulosic material thereby producing a more uniform pulp upon digestion.

Another object of the present invention is to provide a process for substantially eliminating both the air and moisture content of the cellulosic material prior to impregnation.

Still another object of the present invention is to provide improved apparatus for substantially eliminating both the air and moisture content of the cellulosic material.

These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawing which illustrates in the single figure thereof, for purposes of illustration only, a schematic layout of suitable apparatus for carrying out the invention.

Referring now more particularly to the sole figure of the drawing, the major components of the illustrative apparatus include a preheater wherein the wood chips or like cellulosic material is preheated, a drier wherein the preheated chips are dried, a vacuum tank 30 wherein the dried chips are degassed and subsequently submerged 'in cooking liquor to form a chip-liquor suspension, heat 3,215,587 ?atented Nov. 2, 1965 exchangers 4t) and 50 for raising the suspension to the cooking temperature, and a digester 60.

Wood chips or like cellulosic material are introduced into preheater 10 at the open upper end thereof by a conveyor belt or other suitable means, schematically indicated by line 12. Air from line 14 is introduced into the bottom of preheater 10 through spargers or distributors (not shown) and is passed in countercurrent flow to the chips descending through preheater 10. The volume of air being introduced into preheater 10 is sufficient to cause the chips to be maintained as an expanded mass within the preheater 10. The chips are heated by means of steam jackets 16 and 18, which are provided with steam through steam lines 22 and 24, respectively. Condensate is withdrawn from steam jackets 16 and 18 by condensate lines 26 and 28, respectively. Within preheater 10 the chips are heated to a temperature slightly below the boiling point of Water and some or all of the surface moisture on the chips is removed. However, the main object of this treatment is to avoid subsequent condensation in the drier 20. The chips in preheater 10 may be alternatively heated by passing air which has been heated to a temperature sufficient to heat the chips to process temperature thereby eliminating the need for providing the preheater 10 with steam jackets 16 and 18.

Preheated chips are passed from the bottom of preheater 10 through a rotary valve 32 or other suitable feeding and metering device into the upper portion of drier 20. A steam coil 34 or other suitable heating device is positioned within the drier 20 and is supplied with steam through line 36 for drying the chips. Condensate is withdrawn from coil 34 through line 38. Drier 20 is maintained at a pressure slightly above atmospheric pres- F sure and at a temperature whereby a substantial portion of the moisture in the chips is removed as vapor which is vented from the upper portion of drier 20 through line 42. In the process of vaporizing the water contained in the pores of the chips, a substantial portion of the gases occluded within the pores is also removed from the chips. A portion of the vapor in line 42 is recycled to the bottom of drier 20 through line 44, blower 46 which is driven by motor 48, and line 52. The vapor introduced through line 52 causes the chips to form an expanded mass within drier 20.

The remainder of the vapor withdrawn in line 42 is passed through line 54 to a direct contact condenser (not shown) to recover the heat content thereof. Additionally, the water vapor that is withdrawn in line 44 will to a considerable extent displace air from the pores of the chips.

The chips withdrawn from drier 20 are dry and superheated in respect to the saturation temperature of the water vapor therein, and are fed through a rotary valve 56 or other suitable metering device into vacuum tank 30. Tank 30 is maintained at a subatmospheric pressure from about 1 to 5 p.s.i.a. by a vacuum line 58 in communication with a steam jet evacuator 62 which is supplied with steam through line 64. A mass of chips is formed within tank 30 and the residence time of the chips therein is regulated so that the period of time during which the chips are under vacuum insures that substantially all the remaining air and moisture content of the chips is removed through vacuum line 58 to evacuator 62.

Fresh cooking liquor is introduced into tank 30 through line 65 while recycled cooking liquor is introduced through line 66, as more fully hereinafter described. As the body of chips within tank 30 descends through, the degassed chips are submerged in the cooking liquor supplied through lines 65 and 66. The liquor level within tank 30 is maintained within the desired range by suitable liquor level controller and associated valves (not shown).

Should the chips introduced into preheater 1!) be relatively dry, substantially all of the moisture and air initially contained within the pores of the chips will be removed during passage through drier 20. Consequently, the tank need not be maintained under a vacuum and now functions to effect a contact between the chips and cooking liquor.

A chip-liquor suspension of suitable consistency is withdrawn from tank 30 through line 68 by pump 7% and is passed to a multi-pass countercurrent heat exchanger, generally designated by reference numeral 40, wherein the suspension heated by a hot recycled liquor in a recycle line 72. Impregnation of the chips with cooking liquor primarily takes place in multi-pass heat exchanger 40.

The recycled liquor which has been cooled in heat exchanger is withdrawn through line '74 and is passed to heat exchanger 76 for further cooling before introduction into vacuum tank 30 through line 66 to insure that the chips in tank 30 will not be prematurely subjected to cooking temperatures.

From heat exchanger 40, the chip-liquor suspension is passed through line 78 to heat exchanger 50 wherein the suspension is heated to a temperature within the conventional digest-ion temperature range. The heated suspension is passed through line 80 into the top of digester 60 for digestion while submerged in cooking liquor. Liquor in excess of that required for digestion is removed from digester 60 through line 72 for recycle to tank 30 in the manner hereinbefore set forth. If desired, a suitable chip-liquor separator (not shown) may be provided either within digester 60 or exteriorly thereof to facilitate separating excess liquor from the chips and the liquor required in digestion. Digester 60 is provided with a vent line 82 to remove any gas brought in with the chip suspension.

The upper portion of digester 60 essentially constitutes a digestion zone While the lower portion constitutes a leaching zone. The chips introduced into the top of digester 60 descend through the cooking zone and upon the completion of digestion pass into the lower leaching zone. Black liquor is removed from digester 60 through line 84 which is provided with a valve 86.

Wash liquid is introduced into the leaching zone through line 88 provided with a valve 90. The amount of water introduced is sufficient to cause a portion of the wash liquid to pass upwardly in countercur'rent flow to the digested pulp and thereby leaching out spent liquor which is discharged from digester 60 through line 84. The remaining Wash liquid, in addition to leaching liquor from the pulp, dilutes the pulp and the resulting suspension is Withdrawn from the bottom of digester 60 through line 92 provideded with a flow regulating valve 94, or any other suitable metering device, such as a screw press. The pulp may now be further treated in subsequent operations of a conventional nature.

While one embodiment in accordance with the present invention has been shown and described, it will be understood that the same is not limited thereto but is susceptible of many changes and modifications. For example, while the invention has been described in connection with digestion of chips submerged in cooking liquor which is the preferred embodiment, since the excess cooking liquor essentially acts as a flywheel on the temperature so that the desired cooking temperature can be more easily and precisely controlled, it will be apparent that certain features of the present invention could also be advantageously utilized when digestion is carried out in an atmosphere of superheated steam.

It will also be appreciated that in a commercial installation conventional control means in addition to those described for the purpose of illustration may be provided to enable a substantially automatic regulation of the system. Accordingly, it is intended to cover all such changes and modifications as are encompassed by the scope of the appended claims.

I claim:

1. A process for treating cellulosic material comprising forming an expanded mass of cellulosic material, preheating the material to a temperature slightly below the boiling point of water in a first zone so as to drive off surface moisture from said material, introducing the preheated material into a second heated zone, removing part of the moisture and occluded gases in the pores of the material as overhead vapors, recycling a portion of the overhead vapors to a lower region of the second zone to maintain the material in an expanded mass condition, and vacuum degassing the material in a third zone to remove substantially all moisture and gases from said material.

2. A process for treating cellulosic material comprising forming an expanded mass of cellulosic material, preheating material to a temperature slightly below the boiling point of water in a first zone so as to drive off surface moisture from said material, introducing the preheated material into a second heated second zone, removing part of the air and moisture and occluded gases in the pores of the material as overhead vapors, maintaining the material in an expanded mass condition Within the second zone, and vacuum degassing the material in a third zone to substantially all moisture and gases from said material.

3. A process for treating cellulosic material comprising forming an expanded mass of cellulosic material, preheating the material to a temperature slightly below the boiling point of Water in a first zone so as to drive oif surface moisture from said material, introducing the preheated material into a second heated zone, removing part of the moisture and occluded gases in the pores of the material as overhead vapors, recycling a portion of the overhead vapors to a lower region of the second zone to maintain the material in an expanded mass condition, vacuum degassing the material in a third zone to remove substantially all moisture and gases from said material, submerging the degassed material in cooking liquor to form a suspension, introducing the suspension into a digester for digestion therein, and recycling liquor from the digester for use in the submerging step.

4. A process for treating cellulosic material comprising forming an expanded mass of cellulosic material, preheating the material to a temperature slightly below the boiling point of water in a first zone so as to drive off surface moisture from said mate-rial, introducing the preheated material into a second heated zone, removing part of the moisture and occluded gases in the pores of the material as overhead vapors, recycling a portion of the overhead vapors to a lower region of the second zone to maintain the material in an expanded mass condition, vacuum degassing the material in a third zone to remove substantially all moisture and gases from said material, submerging the degassed material in cooking liquor to form a suspension, heating the suspension to digestion temperature, introducing the heated suspension into a digester for digestion therein, and recycling liquor from thedigester for use in the submerging step.

5. A process for treating cellulosic material comprising forming an expanded mass of cellulosic material, pre heating the material to a temperature slightly below the boiling point of water in a first zone so as to drive off surface moisture from said material, introducing the pre heated material into a second heated zone, removing part of the air and moisture in the pores of the material as overhead vapors, maintaining the material in an expanded mass condition within the second zone, vacuum degassing the material in a third zone to remove substantially all the moisture and gases from said material, submerging the degassed material in cooking liquor to form a suspension, introducing the suspension into a digester for digestion therein, and recyling liquor from the digester for use in the submerging step.

6. A process for treating cellulosic material comprising forming an expanded mass of cellulosic material, preheating the material to a temperature slightly below the boiling point of Water in a first zone so as to drive off surface moisture from said material, introducing the preheated material into a second heated zone, removing part of the air and moisture in the pores of the material as overhead vapors, maintaining the material in an expanded mass condition within the second zone, vacuum degassing the material in a third zone to remove substantially all moisture and gases from said material, submerging the degassed material in cooking liquor to form a suspension, heating the suspension to digestion temperature, introducing the heated suspension into a digester for digestion therein, and recycling liquor from the digester for use in the submerging step.

7. A process for treating cellulosic material comprising forming an expanded mass of cellulosic material, preheating the material to a temperature slightly below the boiling point of water in a first zone so as to drive off surface moisture from said material, introducing the preheated material into a second zone, removing substantially all of the moisture and air from the pores of said material, recycling a portion of the vapors from said second zone to maintain the material in an expanded mass condition, submerging said material in cooking liquor to form a suspension, heating the suspension to digestion temperatures, introducing the heated suspension into a digester for digestion therein, and recycling liquor from the digester for use in the submerging step.

8. Apparatus for treating cellulosic material, comprising a preheater including heating means and gas-feeding means in the lower region of said preheater to maintain the material in an expanded mass condition, a drier receiving preheated material from said preheater and including heating means to drive moisture out of said material as an overhead vapor, means to form the material within said drier into an expanded mass, said last mentioned means including means to recycle a portion of the overhead vapor to a lower region of said drier, a vacuum tank for degassing said material to remove air and moisture from the material, means to feed said material from said drier into said vacuum tank, and means to introduce cooking liquor into said vacuum tank to submerge degassed material in cooking liquor to form a chip-liquor suspension.

9. Apparatus for treating cellulosic material, compris ing a preheater including heating means and gas-feeding means in the lower region of said preheater to maintain the material in an expanded mass condition, a drier receiving preheated material from said preheater and including heating means to drive moisture out of said material as an overhead vapor, means to form the material Within said drier into an expanded mass, said last mentioned means including means to recycle a portion of the overhead vapor to a lower region of said drier, a vacuum tank for degassing said material to remove air and moisture from the material, and means to introduce said material from said drier into said vacuum tank.

10. Apparatus for treating cellulosic material, comprising a drier including heating means to drive moisture out of said material as an overhead vapor, gas-feeding means to form the material Within said drier into an expanded mass, said last mentioned means including means to recycle a portion of the overhead vapor to a lower region of said drier, a vacuum tank for degassing said material to remove air and water vapor from said mate-rial, means to feed said material from said drier into said vacuum tank, means to submerge the degassed material in cooking liquor Within said vacuum tank to form a suspension, a digester, means to supply the suspension to said digester, and means to recycle liquor in excess of that required for digestion to said tank from said digester.

11. Apparatus for pulping cellulosic material, comprising a preheater for heating said material to a temperature of about 212 F., gas-feeding means in the lower region of said preheater to maintain the material in said preheater in an expanded mass condition, a drier receiving preheated material from said preheater and including heating means to drive moisture out of said material as an overhead vapor, means to form the material Within said drier into an expanded mass, said last mentioned means including means to recycle a portion of the overhead vapor to a lower region of said drier, a vacuum degasser tank to remove substantially all of the air and moisture content of said material, means to feed said material from said drier into said vacuum tank, means to submerge degassed material in cooking liquor Within said tank to form a suspension, a digester, means to heat the suspension to digestion temperature exteriorly of said digester, means to supply the heated suspension to said digester, and means to recycle liquor in excess of that required for digestion to said tank from said digester.

References Cited by the Examiner UNITED STATES PATENTS 1,413,716 4/22 Fish 16253 1,820,994 9/31 Wallin 162-59 X 2,230,119 1/41 Olsen.

2,640,774 6/53 Ross.

2,668,110 2/54 Spencer 16217 2,675,311 4/54 Natwick 16219 2,870,009 1/59 Richter 162-19 FOREIGN PATENTS 333,426 8/30 Great Britain.

DONALL H. SYLVESTER, Primary Examiner. MORRIS Q. WOLK, Examiner, 

2. A PROCESS FOR TREATING CELLULOSIC MATERIAL COMPRISING FORMING AN EXPANDED MASS OF CELLULOSIC MATERIAL, PREHEATING MATERIAL TO A TEMPERATURE SLIGHTLY BELOW THE BOILING POINT OF WATER IN A FIRST ZONE SO AS TO DRIVE OFF SURFACE MOISTURE FROM SAID MATERIAL, INTRODUCING THE PREHEATED MATERIAL INTO A SECOND HEATED SECOND ZONE, REMOVING PART OF THE AIR AND MOISTURE AND OCCLUDED GASES IN THE PORES OF THE MATERIAL AS OVERHEAD VAPORS, MAINTAINING THE MATERIAL IN AN EXPANDED MASS CONDITION WITHIN THE SECOND ZONE, AND VACUUM DEGASSING THE MATERIAL IN A THIRD ZONE TO SUBSTANTIALLY ALL MOISTURE AND GASES FROM SAID MATERIAL.
 9. APPARATUS FOR TREATING CELLULOSIC MATERIAL, COMPRISING A PREHEATER INCLUDING HEATING MEANS AND GAS-FEEDING MEANS IN THE LOWER REGION OF SAID PREHEATER TO MAINTAIN THE MATERIAL IN AN EXPANDED MASS CONDITION, A DRIER RECEIVING PREHEATED MATERIAL FROM SAID PREHEATER AND INCLUDING HEATING MEANS TO DRIVE MOISTURE OUT OF SAID MATERIAL AS AN OVERHEAD VAPOR, MEANS TO FORM THE MATERIAL WITHIN SAID DRIER INTO AN EXPANDED MASS, SAID LAST MENTIONED MEANS INCLUDING MEANS TO RECYCLE A PORTION OF THE OVERHEAD VAPOR TO A LOWER REGION OF SAID DRIER, A VACUUM TANK FOR DEGASSING SAID MATERIAL TO REMOVE AIR AND MOISTURE FROM THE MATERIAL, AND MEANS TO INTRODUCE SAID MATERIAL FROM SAID DRIER INTO SAID VACUUM TANK. 